Control spring for a fuel injection valve for internal combustion engines

ABSTRACT

A fuel injection valve for internal combustion engines having, a valve member, which is axially displaceable in a valve body and which on one end has a valve sealing face with which it cooperates with a stationary valve seat in order to control an injection cross section, and having at least one valve spring, which urges the valve member in the direction of the valve seat and is braced on its other end on a stationary stop. To increase the spring force of the valve spring while the outer diameter remains the same, the windings of the valve spring, embodied as a helical spring, have a circular basic cross section (Y), which in a region pointing radially outward from the axis (X) of the valve spring has a ground face oriented parallel to the spring axis (X).

PRIOR ART

The invention is based on a fuel injection valve for fuel injectionengines. In one such fuel injection valve, known from German Patent 2943 744, a valve member is guided axially displaceably in a valve body.On one end, toward the combustion chamber, the valve member has a valvesealing face, with which it cooperates with a stationary valve seat onthe valve body for the sake of controlling an injection cross section.On its other end, remote from the combustion chamber, the valve memberis acted upon by a valve spring, which presses the valve member intocontact with the valve seat. This valve spring is inserted into a springchamber inside the housing of the injection valve, in this case in aretaining body, and is braced with its end remote from the valve memberon a stationary stop face. The valve spring is embodied as a helicalspring, whose windings of spring wire have a circular cross section.

The spring force of the valve spring determines the opening pressure atthe injection valve, which is built up from the high fuel pressureengaging the valve member in the opening direction. The capacity orspring force of the valve spring thus has major significance; thisspring force is dependent essentially on the cross-sectional area of thewire at the windings. If the spring force is to be increased, it isusual with conventional round wire to increase the wire thickness, sothat its maximum cross-sectional area is the result of the predeterminedoutside and inside diameter of the winding cross section.

The known fuel injection valve has the disadvantage, however, thatincreasing the wire thickness or axially lengthening the valve spring inorder to increase the spring force meets with structural limits, sincethe existing installation space for the spring chamber is limited andcannot be increased without making extensive changes in the injectionvalve, so that increasing the spring force of the valve spring is notpossible without making complicated changes in the injection valve.

ADVANTAGES OF THE INVENTION

The fuel injection valve according to the invention for internalcombustion engines, has the advantage over the prior art that the springforce of the valve spring can be increased without increasing therequired installation space for the valve spring in the housing of theinjection valve; this advantage is especially pronounced in springs witha very small inside diameter and hence a low winding ratio (Dm/y up to2.5).

This becomes advantageously possible in that the valve spring, embodiedas a helical spring, is made of thicker spring wire with an increasedbasic cross section at the windings and is then ground down on theoutside diameter far enough that the valve spring can just be insertedinto the cylindrical spring chamber, in which it then has only as muchplay relative to the inner wall as is needed when the valve spring iscompressed. The initially circular basic cross section of the springwindings then has ground faces on its ends pointing radially outwardwith respect to the spring axis, and these ground faces are orientedparallel to the spring axis and to the wall of the spring chamber.

In this way, while the installation space for the valve spring remainsthe same, greater opening pressures can be attained, and in the casewhere two valve springs that come into play successively are used, inso-called two-spring holders, greater opening pressure differences canbe achieved.

In addition, the tolerance in terms of the outer diameter of the valvespring can be reduced to a minimum amount, compared with unmachinedsprings.

The valve spring embodied according to the invention has the advantageover alternative wire cross sections, such as rectangular, elliptical orother shaped wires, that the wire production involves no additionalexpense, and the valve spring can thus be produced more easily andeconomically than the aforementioned versions. Moreover, by thesubsequent grinding down of the outer diameter of the valve spring, moreaccurate outer diameters of the spring and thus better utilization ofthe space in the predetermined spring chamber can be achieved.Furthermore, in this way possible flaws in the material on the outerdiameter of the valve spring are simultaneously eliminated.

The use of this optimized spring is not limited to the described use ina fuel injection valve but can instead be applied anywhere that despitea restricted installation space the spring force of a restoring springis to be increased, such as in injection pumps or gas exchange valves ofinternal combustion engines and the like.

Further advantages and advantageous features of the subject of theinvention can be learned from the specification, drawing and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

One exemplary embodiment of the fuel injection valve of the inventionfor internal combustion engines is shown in the drawing and described infurther detail in the ensuing description.

FIG. 1 shows a longitudinal section through the fuel. injection valve,and FIG. 2 shows an enlarged detail of the valve spring of FIG. 1.

DESCRIPTION

In the exemplary embodiment shown in FIG. 1 of the fuel injection valveaccording to the invention for internal combustion engines, a pistonlikevalve member 1 is guided axially displaceably in a bore 3 of a valvebody 5, which on its one end, toward the engine combustion chamber, hasa conical valve sealing face 7, with which it cooperates with a conicalvalve seat 9 on the inward-projecting, closed end of the bore 3. Thevalve body 5 is braced axially by its end remote from the combustionchamber, by means of a tension nut 11, against a valve holding body 13,and a shim 15 with a central opening is fastened between the end facesof the valve body 5 and the valve holding body 13.

On its end remote from the valve seat 9, the valve member 1 is urged viaa pressure pad 17, protruding through the shim 15, in the direction ofthe valve seat 9 by a valve spring 19 embodied as a helical spring,which is inserted into a cylindrical spring chamber 21 in the valveholding body 13 and is braced on its other end on a stationary stop 23formed by the upper axial wall of the spring chamber 21.

Downstream of the sealing seat between the valve sealing face 7 and thevalve seat 9, an injection opening 25 is also provided in the wall ofthe valve body 5; beginning at the bore 3, this opening discharges intothe combustion chamber of the engine to be supplied.

The high-pressure delivery of fuel to the sealing seat is effected in aknown manner via an annular conduit 27, formed between the shaft of thevalve member 1 and the wall of the bore 3; the annular conduit widens inthe region of an annular shoulder 31 of the valve member 1 to form apressure chamber 29, into which a pressure line 33, leading away from aninjection pump, not shown, discharges.

To increase the spring force while the outer dimensions remain the same,the valve spring 19, as shown on a larger scale in FIG. 2, has groundface 43, which are oriented parallel to the spring axis X and to theinner wall of the cylindrical spring chamber 21, on the ends pointingradially outward from the spring axis X of the circular-annular basiccross section y of its spring windings 41 which are wound in a spiral.

The valve spring 19 is first made from a round spring wire with such alarge cross section y that the theoretical outside diameter of theunmachined valve spring 19 is larger than the inside diameter of thespring chamber 21. In a subsequent operation, so much material isremoved, preferably being ground off, from the outer diameter of thevalve spring that the valve spring 19 is just barely insertable, withthe requisite play, into the spring chamber 21.

The remaining cross-sectional area z of the spring windings 41 is stillsignificantly greater, despite the ground faces 43, than thecross-sectional area of an unmachined valve spring with annular springwire with the identical outside diameter, so that the attained springforce of the valve spring 19 can be increased considerably withoutrequiring additional installation space.

The ratio y/z is preferably in a range from 1.05/1 to 1.3/1.

It would be obvious to one skilled in the art that a prior art springwould have spirals with a cylindrical cross section from the innerdiameter to the ground face 43 so that the spiral would be smaller indiameter.

The foregoing relates to preferred exemplary embodiments of theinvention, it being understood that other variants and embodimentsthereof are possible within the spirit and scope of the invention, thelatter being defined by the appended claims.

The invention claimed and desired to be by Letters Patent of the UnitedStates is:
 1. A fuel injection valve for internal combustion enginescomprising a valve member (1), which is axially displaceable in a valvebody (5) and which on one end has a valve sealing face (7) with whichsaid valve member (1) cooperates with a stationary valve seat (9) inorder to control an injection cross section, and a valve spring chamber(21), a valve spring (19) is embodied as a helical spring with acircular basic cross section (Y), in which said valve spring has anormal outer diameter (da) which is greater than a diameter of saidvalve spring chamber (21) and having a spring axis (X), each saidwinding of said valve spring has a ground down outer flat radial surfaceface in which said valve spring has a reduced diameter which is lessthan an inside diameter of said valve spring chamber and placed in saidvalve spring chamber with said surface faces oriented in a planeparallel with the spring axis (X) and in parallel with a wall of saidvalve spring chamber, said valve spring is braced at one end on one endof said valve member and another end is braced on a stationary stop(23), said valve spring urges the valve member 1 in a direction of thevalve seat (9), and said valve spring has a slight play with respect tothe inside diameter of said spring chamber (21).
 2. A fuel injectionvalve in accordance with claim 1, in which a ratio y/z of the valvespring (19) is a range of from 1.05/1 to 1.3/1.